1. Field of the Invention
The present invention relates to an internal combustion engine storage-volume fuel injection system.
2. Description of the Related Art
Modern internal combustion engine fuel injection systems normally comprise a pump for supplying high-pressure fuel to a common rail having a given fuel storage volume and for supplying a number of engine cylinder injectors. The pump comprises at least one reciprocating pumping element performing each time an intake stroke and a compression or delivery stroke.
As is known, for it to be atomized properly, the fuel must be brought to extremely high pressure, e.g. in the region of 1600 bars in maximum engine load conditions. Current regulations governing pollution by engine exhaust gas require that the fuel feed pressure to the injectors be reproducible as accurately as possible with respect to the electronic central control unit map. Pressure fluctuations, in the common rail, with respect to the set pressure can be limited if the volume of the common rail is over order of magnitude of the fuel quantity drawn by each injector per combustion cycle. Such a common rail, however, is invariably bulky and therefore difficult to accommodate on the engine.
To control pressure in the common rail as mapped in the central control unit, it has been proposed to fit, along the pump delivery conduit to the common rail, a bypass solenoid valve controlled by an electronic unit as a function of various engine operating parameters. It has also been proposed to operate the pumping element by means of cam operating synchronously with each injector.
In known systems of this sort, each pumping element has an instantaneous flow, the maximum value of which is less than the maximum value of each injector, so that, during each injection, only part of the injected fuel, about 20%, is normally supplied by the pump, the rest being supplied by the common rail. Systems of this sort therefore have the drawback of necessarily requiring a common rail of suitable size. Moreover, the pump operates permanently at the maximum flow rate, while the bypass solenoid valves simply provides for draining the surplus pumped fuel, in excess of that drawn by the injectors, into the tank, thus dissipating heat.